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Old December 30th, 2017, 11:25 AM
James James is offline
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Join Date: Jun 2013
Location: Greer, SC
Truck: 1964 GMC 1500 2wd
Age: 69
Posts: 432
Rep Power: 199
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Default Re: Regarding vacuum advance and timing

In my 62 manual it states to disconnect the vacuum line (did not say to plug it) and set the 305D to 7-1/2° BTC. This information came out of the electrical section of the manual.

On my truck with a Stromberg carburetor (it only has one vacuum port), it is ported vacuum and not manifold vacuum. With the engine at it proper idle setting the throttle valve is not open enough to supply vacuum to the distributor.

With the vacuum line disconnected and the warm engine at proper idle speed does your line has vacuum on it? If it does not then increasing the engine rpm can you feel the vacuum? If this is the case then you have ported vacuum.

Manifold vacuum is there all the time no matter what the engine idle speed is set to.

The correct way to set the distributer is to disconnect the vacuum line and plug it. This way no matter which type of supply vacuum you have it will not affect the timing.

Last edited by James; December 30th, 2017 at 12:03 PM. Reason: Added more info
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